Some of the larger broadband providers in the UK have already changed their advertising; for example, BT now advertises its fibre-based Infinity service as up to 38Mbps rather than 40Mbps, as previously.

Other providers, such as Virgin Media, have not changed the advertised headline speed for its packages. The company told ZDNet UK on Tuesday that Ofcom has shown that it regularly delivers its claimed speeds. Additionally, the company also provides detailed average speed information for customers on each of its packages.

Smaller ISPs that primarily offer copper-based ADSL and ADSL2+ services, like Be Broadband, are also yet to reflect the changes in advertising regulation on packages.

An Ofcom report in February on the average UK fixed-line internet speeds found that cable and fibre-based services such as BT Infinity and Virgin Media's super-fast packages were more likely to achieve the advertised headline speeds than copper-line services.

According to an industry expert, under the new rules an ISP that advertises a package using a speed claim is also obliged to reveal any details about traffic shaping, known as throttling, which the connection may be subject to under certain conditions. Conversely, not advertising a package by speed means that ISPs are not obliged to reveal these details, ZDNet UK understands. The ASA had not responded to a request for clarification at the time of writing.